From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D711FC4320A for ; Mon, 16 Aug 2021 00:11:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B4A44613A7 for ; Mon, 16 Aug 2021 00:11:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231883AbhHPAMN (ORCPT ); Sun, 15 Aug 2021 20:12:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38986 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231668AbhHPAMG (ORCPT ); Sun, 15 Aug 2021 20:12:06 -0400 Received: from mail-il1-x149.google.com (mail-il1-x149.google.com [IPv6:2607:f8b0:4864:20::149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 03722C061764 for ; Sun, 15 Aug 2021 17:11:36 -0700 (PDT) Received: by mail-il1-x149.google.com with SMTP id y8-20020a92c748000000b00224811cb945so690024ilp.6 for ; Sun, 15 Aug 2021 17:11:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=J0lJJJkW+NmZlpb6fpFofwzCF2N0YPn/fE7VW8sEN0E=; b=onMRm+c0TmbvvH91s8krImCv1CKEk4b274WYjrqgKk7gKLOUw9VrXJClkZ1DmSna/8 3tepivV3mzLKvagWxhpO+/WQdfkPceIPNKfBb2bGq51hsXJu/WQCIkjs874UB7dk0W9W oXAUvi79qPx6l8QqPRpDusbWhyXuCw7E1AogPxUA0fgJz83AKxK+/O+IR3aKYsxFeqZM JjNSmzkGS23X+RekEHj1AacWn1arDI/RxjwhBttOKfWKf9+zoiG8nYGaSZvEuGaZs74t Vs8UyftyhM2f38KfhifByPOjskfYoVIv781b+80yLp+3M+udeuw+Zi4uFZAtu/XHAmkx u6/g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=J0lJJJkW+NmZlpb6fpFofwzCF2N0YPn/fE7VW8sEN0E=; b=U1h8Q0rQQ3Q6b+6r7bB4hRZ8RxwK9GWQVTaBz2jwXmaRkzWdGLiKj67j7yBwoBBzsh eEzgn1spK034XQomzQWt3cBqiRzx75j2ONjeMvaSKo5Zqe+3f7Ubp7S52+SKhfMnRJy0 zHXi0Oc21v931PISpXuM9PcxZlKc7lx+qklIA/BO+/XRzRZpgPs0lBxQL5Zb4BW0RtsE MSpCdCNfZxEu5Knh9au0QpTmHUFhC/XJ/E5zhIIHHZmuWraRs138NFh1wuI/RZJeq4lU cpKhIAfg+lvyG4fGgSggelkrwrHfKUa9leS9XKuXsMvTPx4TGNH2zrhJ4wJmN0fV54vJ Yw+A== X-Gm-Message-State: AOAM531h/kB0GLQDRGOyEnW78T1mUY1cNPqeGHw7mJp1qkTzvi334uuW A9uD/s+iiuFe/SXtRpZp3j+n5+6Z+1RQRpGcSI5WNSgs095qC++ptnvXmQqnAqI2B5ZbxGGDG/H 2fX8KXa+DLUi2NcdnCiLfNUIF6uvQLoOwYmjMo+lbcCeZq0T+z+VBeLS/+w== X-Google-Smtp-Source: ABdhPJw09eGgNy3EXbjdqGFxxJgFJV5YrUuGjNKkF5zMC9eqOSxrLDgPkbJpMCJxluIG+Ci2XveMUkYVc70= X-Received: from oupton.c.googlers.com ([fda3:e722:ac3:cc00:2b:ff92:c0a8:404]) (user=oupton job=sendgmr) by 2002:a02:cd09:: with SMTP id g9mr12684753jaq.87.1629072695306; Sun, 15 Aug 2021 17:11:35 -0700 (PDT) Date: Mon, 16 Aug 2021 00:11:25 +0000 In-Reply-To: <20210816001130.3059564-1-oupton@google.com> Message-Id: <20210816001130.3059564-2-oupton@google.com> Mime-Version: 1.0 References: <20210816001130.3059564-1-oupton@google.com> X-Mailer: git-send-email 2.33.0.rc1.237.g0d66db33f3-goog Subject: [PATCH v7 1/6] KVM: x86: Fix potential race in KVM_GET_CLOCK From: Oliver Upton To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu Cc: Paolo Bonzini , Sean Christopherson , Marc Zyngier , Peter Shier , Jim Mattson , David Matlack , Ricardo Koller , Jing Zhang , Raghavendra Rao Anata , James Morse , Alexandru Elisei , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, Andrew Jones , Will Deacon , Catalin Marinas , Oliver Upton Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Sean noticed that KVM_GET_CLOCK was checking kvm_arch.use_master_clock outside of the pvclock sync lock. This is problematic, as the clock value written to the user may or may not actually correspond to a stable TSC. Fix the race by populating the entire kvm_clock_data structure behind the pvclock_gtod_sync_lock. Suggested-by: Sean Christopherson Signed-off-by: Oliver Upton --- arch/x86/kvm/x86.c | 39 ++++++++++++++++++++++++++++----------- 1 file changed, 28 insertions(+), 11 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index fdc0c18339fb..2f3929bd5f58 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2787,19 +2787,20 @@ static void kvm_update_masterclock(struct kvm *kvm) kvm_end_pvclock_update(kvm); } -u64 get_kvmclock_ns(struct kvm *kvm) +static void get_kvmclock(struct kvm *kvm, struct kvm_clock_data *data) { struct kvm_arch *ka = &kvm->arch; struct pvclock_vcpu_time_info hv_clock; unsigned long flags; - u64 ret; spin_lock_irqsave(&ka->pvclock_gtod_sync_lock, flags); if (!ka->use_master_clock) { spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags); - return get_kvmclock_base_ns() + ka->kvmclock_offset; + data->clock = get_kvmclock_base_ns() + ka->kvmclock_offset; + return; } + data->flags |= KVM_CLOCK_TSC_STABLE; hv_clock.tsc_timestamp = ka->master_cycle_now; hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset; spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags); @@ -2811,13 +2812,26 @@ u64 get_kvmclock_ns(struct kvm *kvm) kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL, &hv_clock.tsc_shift, &hv_clock.tsc_to_system_mul); - ret = __pvclock_read_cycles(&hv_clock, rdtsc()); - } else - ret = get_kvmclock_base_ns() + ka->kvmclock_offset; + data->clock = __pvclock_read_cycles(&hv_clock, rdtsc()); + } else { + data->clock = get_kvmclock_base_ns() + ka->kvmclock_offset; + } put_cpu(); +} - return ret; +u64 get_kvmclock_ns(struct kvm *kvm) +{ + struct kvm_clock_data data; + + /* + * Zero flags as it's accessed RMW, leave everything else uninitialized + * as clock is always written and no other fields are consumed. + */ + data.flags = 0; + + get_kvmclock(kvm, &data); + return data.clock; } static void kvm_setup_pvclock_page(struct kvm_vcpu *v, @@ -6098,11 +6112,14 @@ long kvm_arch_vm_ioctl(struct file *filp, } case KVM_GET_CLOCK: { struct kvm_clock_data user_ns; - u64 now_ns; - now_ns = get_kvmclock_ns(kvm); - user_ns.clock = now_ns; - user_ns.flags = kvm->arch.use_master_clock ? KVM_CLOCK_TSC_STABLE : 0; + /* + * Zero flags as it is accessed RMW, leave everything else + * uninitialized as clock is always written and no other fields + * are consumed. + */ + user_ns.flags = 0; + get_kvmclock(kvm, &user_ns); memset(&user_ns.pad, 0, sizeof(user_ns.pad)); r = -EFAULT; -- 2.33.0.rc1.237.g0d66db33f3-goog